RF through water question

What are the design issues involved with passing medium wave ( 10s of MHz ) higher power ( KWatts) RF through a water jacket. Assume "tap" water and of
course non conductive non ferrous housing material.
Ron H.
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Ron H. wrote:

Checkout: http://www.qsl.net/vk5br/UwaterComms.htm
--
Scott

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Um.. unless your water is de-ionized or distilled, you don't pass RF through it. It gets absorbed and turned into heat just like in a microwave oven. Tap water is not de-ionized.
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snipped-for-privacy@usa.net wrote:

How do you think they talk to submarines? (the answer is: slowly!) You can pass RF through water (even sea water), but unless it's very low frequency (or extremely low - ELF) it doesn't get very far. You'd get serious attenuation with 10s of MHz.
Tim
--
Love is a travelator.

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Tim Auton wrote...

For the most part, with acoustic signaling. And sub-20kHz ELF, but only if the sub is near the surface and trailing an antenna.
Thanks, - Win
(email: use hill_at_rowland-dot-org for now)
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AFAIK VLF (3-20kHz) is only used near the surface with a trailing antenna, but the latest ELF systems have neither requirement. What I can find on the ELF system in use by the US (76Hz) suggests they can receive ELF at operational speed and depth, which doesn't suggest "near the surface" to me. It's all relative of course and hard figures are hard to come by (hardly surprising!), but I've seen 2-300m mentioned. AIUI they use on/in-hull antennas (presumably SQUID based) instead of trailing wire antennas for ELF too.
OK, perhaps it's not how they /usually/ talk to submarines though :)
Tim
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Love is a travelator.

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"The other John Smith" in message

You're damn right it does. (The intuitive notion of a tight relationship between bit rate and analog bandwidth disappears like parted waters if you study communication theory -- you can have data rates far greater or far less than bandwidths, in exchange for requirements for SNR or other constraints.) But the subject tends to the counterintuitive, so it collects notions and suppositions and opinions. (Like various other areas of electronics.) This by the way is partly the domain of the newsgroup comp.dsp .
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On Tue, 11 May 2004 23:34:01 -0700, "Max Hauser"

Is this why QAM 256 is far better than simple modulation schemes?
I mean it allows for so much more *use* of the signal as it is being sent.
Anyway, this is party why one can get so many more channels per transponder on a comm bird than was available in the past. That 6MHz wide channel is being filled to the brim with data (and that data compressed as well), as opposed to the signals they repeated in the 60s and 70s.
Thank God for General Instrument (now a division of Motorola).
They (along with others) brought you wide screen form factors, MPEG-2, and HDTV. As well as twelve channel per carrier uplink encoding and decoding. They made your Video/TV life over ten times richer.
GI was not just another cable box maker.
Then the Cable Cos ream us up the ass with their pricing. All the while letting their hardware age, and fester, instead of keeping up. They call that "a good value service".
Cox's news server is one fine example. I'd be surprised if it is even one terabyte in archive size.
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I thought they became microchip?
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On Thu, 13 May 2004 23:15:17 -0500, "Dave VanHorn"

Motorola only bought the uplink encoder division from what I know... which is not exactly what happened... :]
GI has been around for decades, they bought the encoder division which was formerly an arm of Titan/ Linkabit. Or was them.
Anyway... thank them and Woo Paik in particular (now in S. Korea as Pres of his own company) specifically for HDTV in digital form. Were it not for them, the idiots in the consortium would have made an analog version... Oh boy.
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[snipped]

I bet they're mightily pissed off by HTML messages.
Cheers
--
Keith Wootten


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Keith Wootten wrote...

Yes, and no binary attachements allowed.
Thanks, - Win
(email: use hill_at_rowland-dot-org for now)
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On Wed, 12 May 2004 13:03:19 +0100, Keith Wootten

bet they get rid of popup ads as well
martin
Three things are certain: Death, taxes and lost data. Guess which has occurred.
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On Wed, 12 May 2004 15:53:33 +0200, martin griffith

Not to mention a powerful spamfilter.
- YD.
--
Remove HAT if replying by mail.

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On a sunny day (Wed, 12 May 2004 13:03:19 +0100) it happened Keith Wootten

LOL
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A teacher at my college told me that somewhere (i cant have been listening) they use the granite rock as an antenna, and then drill down however amny miles apart and make a connection.
not sure if he was talking aout of his...
Tim
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Actually it could not be much of a secret when people were lighting thier homes with the signal off the antenna.

listening)
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(Amazon.com product link shortened)
I just picked up this one, having read "blind man's bluff" recently.
The chapter on "Hunt for Red October" was rather chilling, as I was living in Hawaii at the time.
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On Wed, 12 May 2004 04:36:27 GMT, "The other John Smith"

This reminds me of another example of the extreme end of communications theory. A couple years ago I interviewed with a company that makes remote readable electric meters. They put a module in the bottom of the meter that reads and counts the rotation of the disk and sends a signal back to equipment placed at certain places around the power grid to collect meter readings.
The signals were sent over the power grid in a band of something like 10 or 20 Hz centered around 60 Hz so it could get through transformers. They crammed thousands of parallel data channels hundredths of a Hz apart into that band. Time to transmit ONE BIT was something like 20 minutes.
They claimed in testing they had received the signal up to 100 miles away.
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About 30 years ago I worked with a fellow who joked: "There are just as many octaves BELOW one hertz as there are ABOVE one hertz."
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